I saw another report claiming the same thing and it was closed because the mods "haven't received any similar reports and we have made a lot of updates recently".

But I have been playing unranked team duels with this person https://www.geoguessr.com/user/627962c3d362f7eedde8af5b for months and they haven't gained any xp from it. As you can see in the stats, they have played 337 unranked team duels and are still only level 8, while I have gained about 150 xp per game from those duels, so the bug is definitely real and should be looked into.